X-ray spectrometry: a powerful tool for the measurement of complete fusion of weakly bound nuclei

We describe how the method of detection of delayed K x-rays produced by the electron capture decay of the residual nuclei can be a powerful tool in the investigation of the effect of the breakup process on the complete fusion (CF) cross-section of weakly bound nuclei at energies close to the Coulomb barrier. This is presently one of the most interesting subjects under investigation in the field of low-energy nuclear reactions, and the difficult experimental task of separating CF from the incomplete fusion (ICF) of one of the breakup fragments can be achieved by the x-ray spectrometry method. We present results for the fusion of the (9)Be + (144)Sm system. Copyright (c) 2008 John Wiley & Sons, Ltd.

Proton-halo effects in the (8)B+(58)Ni reaction near the Coulomb barrier

Elastic scattering of (8)B and (7)Be on a (58)Ni target has been measured at energies near the Coulomb barrier. The total reaction cross sections were deduced from Optical-model fits to the experimental angular distributions. Comparison with other systems shows evidence for proton-halo effects on (8)B, as well as for neutron-halo on (6)He reactions. While the enhancement in the cross section observed for (8)B is explained in terms of projectile breakup, in the case of (6)He reactions, the particle transfer proces explains the observed enhancement.

Scales of critically stable few-body halo systems

We review the scaling properties of few-body observables near the critical conditions for binding, with particular attention to light exotic nuclei, molecules and ultracold atoms.

Neutron-neutron correlations in light exotic nuclei

For light exotic nuclei modeled as two neutrons n and a core A, we report results for the two-neutron correlation functions and also for the mean-square radii, considering a universal scaling function. The results of our calculations for the neutron-neutron correlation functions are qualitatively consistent with recent data obtained for 11Li and 14Be nuclei. The root-mean-square distance in the halo of such nuclei are also consistent with data, which means that the neutrons of the halo have a large probability to be found outside the interaction range. Therefore the low-energy properties of these halo neutrons are, to a large extend, model independent as long as few physical input scales are fixed. The model is restricted to s-wave subsystems, with small energies for the bound or virtual states. For the radii we are also shown results for the 6He and 20C. All the interaction effects, as higher partial wave in the interaction and/or Pauli blocking effect are, to some extend, included in our model, as long as the three-body binding energy is supplied. © 2005 American Institute of Physics.

Complete fusion enhancement and suppression of weakly bound nuclei at near barrier energies

We consider the influence of breakup channels on the complete fusion of weakly bound systems in terms of dynamic polarization potentials. It is argued that the enhancement of the cross section at sub-barrier energies may be consistent with recent experimental observations that nucleon transfer, often leading to breakup, is dominant compared to direct breakup. The main trends of the experimental complete fusion cross sections are analyzed in the framework of the DPP approach. The qualitative conclusions are supported by CDCC calculations including a sequential breakup channel, the one neutron stripping of Li-7 followed by the breakup of Li-6.

Study of electromagnetic reactions on light nuclei with the Lorentz Integral Transform method

In dieser Arbeit aus dem Bereich der Wenig-Nukleonen-Physik wird die neu entwickelte Methode der Lorentz Integral Transformation (LIT) auf die Untersuchung von Kernphotoabsorption und Elektronenstreuung an leichten Kernen angewendet. Die LIT-Methode ermoeglicht exakte Rechnungen durchzufuehren, ohne explizite Bestimmung der Endzustaende im Kontinuum. Das Problem wird auf die Loesung einer bindungzustandsaehnlichen Gleichung reduziert, bei der die Endzustandswechselwirkung vollstaendig beruecksichtigt wird. Die Loesung der LIT-Gleichung wird mit Hilfe einer Entwicklung nach hypersphaerischen harmonischen Funktionen durchgefuehrt, deren Konvergenz durch Anwendung einer effektiven Wechselwirkung im Rahmem des hypersphaerischen Formalismus (EIHH) beschleunigt wird. In dieser Arbeit wird die erste mikroskopische Berechnung des totalen Wirkungsquerschnittes fuer Photoabsorption unterhalb der Pionproduktionsschwelle an 6Li, 6He und 7Li vorgestellt. Die Rechnungen werden mit zentralen semirealistischen NN-Wechselwirkungen durchgefuehrt, die die Tensor Kraft teilweise simulieren, da die Bindungsenergien von Deuteron und von Drei-Teilchen-Kernen richtig reproduziert werden. Der Wirkungsquerschnitt fur Photoabsorption an 6Li zeigt nur eine Dipol-Riesenresonanz, waehrend 6He zwei unterschiedliche Piks aufweist, die dem Aufbruch vom Halo und vom Alpha-Core entsprechen. Der Vergleich mit experimentellen Daten zeigt, dass die Addition einer P-Wellen-Wechselwirkung die Uebereinstimmung wesentlich verbessert. Bei 7Li wird nur eine Dipol-Riesenresonanz gefunden, die gut mit den verfuegbaren experimentellen Daten uebereinstimmt. Bezueglich der Elektronenstreuung wird die Berechnung der longitudinalen und transversalen Antwortfunktionen von 4He im quasi-elastischen Bereich fuer mittlere Werte des Impulsuebertrages dargestellt. Fuer die Ladungs- und Stromoperatoren wird ein nichtrelativistisches Modell verwendet. Die Rechnungen sind mit semirealistischen Wechselwirkungen durchgefuert und ein eichinvarianter Strom wird durch die Einfuehrung eines Mesonaustauschstroms gewonnen. Die Wirkung des Zweiteilchenstroms auf die transversalen Antwortfunktionen wird untersucht. Vorlaeufige Ergebnisse werden gezeigt und mit den verfuegbaren experimentellen Daten verglichen.

Scales of critically stable few-body halo systems

We review the scaling properties of few-body observables near the critical conditions for binding, with particular attention to light exotic nuclei, molecules and ultracold atoms.

The Milky Way's Dark Matter Halo Appears To Be Lopsided

The atomic hydrogen gas (H I) disk in the outer region (beyond similar to 10 kpc from the center) of Milky Way can provide valuable information about the structure of the dark matter halo. The recent three-dimensional thickness map of the outer H I disk from the all sky 21 cm line Leiden/Argentine/Bonn survey, gives us a unique opportunity to investigate the structure of the dark matter halo of Milky Way in great detail. A striking feature of this new survey is the north-south (N-S) asymmetry in the thickness map of the atomic hydrogen gas. Assuming vertical hydrostatic equilibrium under the total potential of the Galaxy, we derive the model thickness map of the H I gas. We show that simple axisymmetric halo models, such as softened isothermal halo (producing a flat rotation curve with V-c similar to 220 km s(-1)) or any halo with density falling faster than the isothermal one, are not able to explain the observed radial variation of the gas thickness. We also show that such axisymmetric halos along with different H I velocity dispersion in the two halves, cannot explain the observed asymmetry in the thickness map. Amongst the nonaxisymmetric models, it is shown that a purely lopsided (m = 1, first harmonic) dark matter halo with reasonable H I velocity dispersion fails to explain the N-S asymmetry satisfactorily. However, we show that by superposing a second harmonic (m = 2) out of phase onto a purely lopsided halo, e. g., our best fit and more acceptable model A (with parameters epsilon(1)(h) = 0.2, epsilon(2)(h) = 0.18, and sigma(H I) = 8.5 km s(-1)) can provide an excellent fit to the observation and reproduce the N-S asymmetry naturally. The emerging picture of the asymmetric dark matter halo is supported by the. cold dark matter halos formed in the cosmological N-body simulation.

Effect of deprivation of vitamin A on the basic proteins of the nuclei of rat testes

The relative concentrations of the major histones, namely, H1, TH1, H2A, H2B, H3 and H4 are not significantly changed in the testes of the vitamin A-deficient rats, as compared to those in the normal controls. But the testis-specific protein, TP, which is synthesized at the mid-spermatid stage, is markedly reduced in the testes of the deficient rats. On supplementation of the deficient rats with retinyl acetate for 28 days, there was a 50% recovery in the relative concentration of the TP with respect to the total amounts of H1 and TH1.

Electrophoretic mobility of cell nuclei (EMN index) as a biomarker of the biological aging process: Considering the association between EMN index and age

The present study examined whether a specific property of cell microstructures may be useful as a biomarker of aging. Specifically, the association between age and changes of cellular structures reflected in electrophoretic mobility of cell nuclei index (EMN index) values across the adult lifespan was examined. This report considers findings from cross sections of females (n = 1273) aged 18–98 years, and males (n = 506) aged 19–93 years. A Biotest apparatus was used to perform intracellular microelectrophoresis on buccal epithelial cells collected from each individual. EMN index was calculated on the basis of the number of epithelial cells with mobile nuclei in reference to the cells with immobile nuclei per 100 cells. Regression analyses indicated a significant negative association between EMN index value and age for men (r = −0.71, p < 0.001) and women (r = −0.60, p < 0.001); demonstrating a key requirement that must be met by a biomarker of aging. The strength of association observed between EMN index and age for both men and women was encouraging and supports the potential use of EMN index for determining a biological age of an individual (or a group). In this study, a new attempt of complex explanation of cellular mechanisms contributing to age related changes of the EMN index was made. In this study, a new attempt of complex explanation of cellular mechanisms contributing to age related changes of the EMN index was made. EMN index has demonstrated potential to meet criteria proposed for biomarkers of aging and further investigations are necessary.

RNA polymerase activity in isolated nuclei of Nicotiana sanderae callus: Characteristics and modulation during differentiation

Isolated nuclei from differentiating cultures of Nicotiana sanderae showed increased levels of RNA polymerase activity as compared to the nuclei from callus cultures. The RNA synthetic activity was dependent on nucleotide triphosphates and Mg2+ and was destroyed by RNase. Maximum activity was obtained in the presence of 50 mM (NH4)2 SO4 and α-amanitin inhibited 40% and 55% of the activity in the nuclei from callus and differentiating tissue respectively. The nuclei from differentiating tissue elicited a 3-fold increase in RNA polymerase I and a 4-fold augmentation in RNA polymerase II activities.